I've created a USB stick of Kali Live, latest version (2004.4). This works fine. In the startup menu I'm using the first option: standard Kali (not Forensic, not persistence).
The problem is the default keyboard layout. I know I can change the layout in the UI or via the command line ("setxkbmap -layout 'ch(de)' to Swiss German keyboard layout), but I want this permanently stored. Of course I could configure persistence and use that boot option, but that's not what I want. I want the default boot option to contain that ch(de) keyboard layout.
I found that this is probably configured in /etc/default/keyboard (in there is "us"), but this file is not persisted of course, so it's gone on the next boot. But I also cannot find this file on the USB drive to permanently overwrite it. Not sure where this comes from. I assume it's in some archive which gets unpacked upon booting or something.
I found that I could of course create a custom Kali image with other packages etc., but just to change the keyboard layout, I think that is overkill. There must be an easier way.
I found that many other users have the same problem, but I couldn't find any answer after searching for hours. I've done this on my old Kali Live installation somehow (years ago, now deleted), but I don't remember how.